Hydrofluoroolefins (HFOs), such as tetrafluoropropenes (including 2,3,3,3-tetrafluoropropene (HFO-1234yf)), are now known to be effective refrigerants, fire extinguishants, heat transfer media, propellants, foaming agents, blowing agents, gaseous dielectrics, sterilant carriers, polymerization media, particulate removal fluids, carrier fluids, buffing abrasive agents, displacement drying agents and power cycle working fluids. Unlike chlorofluorocarbons (CFCs) and hydrochlorofluorocarbons (HCFCs), both of which potentially damage the Earth's ozone layer, HFOs do not contain chlorine and, thus, pose no threat to the ozone layer. HFO-1234yf has also been shown to be a low global warming compound with low toxicity and, hence, can meet increasingly stringent requirements for refrigerants in mobile air conditioning. Accordingly, compositions containing HFO-1234yf are among the materials being developed for use in many of the aforementioned applications.
One known precursor used to prepare HFO-1234yf is 2-chloro-1,1,1,2-tetrafluoropropane (HCFC-244bb). Indeed, there are numerous gas phase reactions that are known for the production of HFO-1234yf by HCFC-244bb dehydrochlorination. U.S. Pub. No. U.S. 2007/0197842, for example, teaches the synthesis of HFO-1234yf through gas phase HCFC-244bb dehydrochlorination in the presence of a carbon- and/or metal-based catalyst (e.g. nickel or palladium based catalysts). U.S. Pub. No. U.S. 2009/0043136 also teaches the preparation of HFO-1234yf through gas phase HCFC-244bb dehydrochlorination in the presence of a catalyst selected from the group consisting of (i) one or more metal halides, (ii) one or more halogenated metal oxides, (iii) one or more zero-valent metals/metal alloys, or (iv) a combination of two or more of the foregoing.
While the foregoing reactions disclose processes having relatively high conversion levels, such reactions are not without disadvantages. As illustrated herein, known processes for the production of HCFC-244bb often produce only about a 90% yield. Thus, the remainder of the product stream includes undesirable by-products and raw materials. These by-products and raw materials are surprisingly shown herein to have a detrimental impact on the ability to produce high purity HFO-1234yf when used in connection with one or more of the applications mentioned above. As a result, they reduce product yields and increase associated costs.
Based on the foregoing, there is a continuing need for an improved process of preparing high purity HFO-1234yf from HCFC-244bb. The instant invention and the embodiments presented herein addresses at least this need.